im too retarded to explain it well but, a pub is like a traditional community rendezvous point where everyone locally goes to have some drinks and chit chat with their friends. in central london its where people go for a pint after work. its chill, there is either no or quiet music. they look very distinct from the outside, inside is usually always wooden. they have names like "the red lion" "the shakespears head" "the viaduct" "the black horse" etc. people go to their local pub to have a sunday roast.
pubs look like pic rel.
so culturally having some pints at the pub is just youll be sitting drinking and talking (of course there are random lively nights and also on special occasions) also people will go to the pub for pre drinks before they go to a bar/club, because drinks in the pub are probably cheaper, they'll leave the pub at 11 or 12, when the pub stops serving drinks, then closes, to go on to a bar/club.
then i guess bar to nightclub is basicallya spectrum of the louder the music is and the later it closes the more of a nightclub it is, they're usually more modern looking, probably serve cocktails, music is louder, there are less seats, theres a dancefloor type area, and theyre open till late, there may be an entry fee, you go here to chat up some SLAGS. which you can do in the pub also but the bar/club is just more appropriate.
an example of a bar chain (there are better independent bars than this shite im just using it as an example) would be like, be at one, turtle bay... stuff like that.
the inbetween a club and a bar is like The Roxy, Simmons Bar, which close at like 3-4.
then a nightclub is like Fabric, which is open till 6am.
honestly im retarded i hope someone comes in and refines what i said to make it more clear